netdev - RE: [PATCH 4/7] net/packet: Ask driver for protocol if not provided by user

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Date:   Thu, 17 Jan 2019 09:10:13 +0000
From:   Maxim Mikityanskiy <maximmi@...lanox.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
CC:     "David S. Miller" <davem@...emloft.net>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Jason Wang <jasowang@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Eran Ben Elisha <eranbe@...lanox.com>,
        Tariq Toukan <tariqt@...lanox.com>
Subject: RE: [PATCH 4/7] net/packet: Ask driver for protocol if not provided
 by user

> > > +static void packet_parse_headers(struct sk_buff *skb, struct socket
> *sock)
> > > +{
> > > +       if (!skb->protocol && sock->type == SOCK_RAW) {
> > > +               skb_reset_mac_header(skb);
> > > +               skb->protocol = dev_parse_header_protocol(skb);
> > > +       }
> > > +
> > > +       skb_try_probe_transport_header(skb);
> > > +}
> >
> >
> > In relation to the discussion at
> >
> >   af_packet: fix raw sockets over 6in4 tunnel
> >   http://patchwork.ozlabs.org/patch/1023623/
> >
> > if adding a new header_ops callback to parse link layer headers,
> > please have it return both protocol and link layer header length.

Sorry, I miss the point here, can you elaborate more? If all you need is
to have some header_ops callback that returns the L2 header length,
there is one already, it's called parse. Or do you have a specific
reason why you want my callback to also return the header length?

> This could just be an extension of existing header_ops->validate.

If you suggest extending an existing function, parse looks more
suitable, but I decided not to touch the existing ones for two reasons:

1. I don't want to break the existing code that uses the parse function
and will need to be modified to pass an extra parameter.

2. I don't want to spend machine time on copying the destination MAC
when I only need the protocol, and vice versa.

I'm looking forward to hearing your thoughts about it.